Blowing agents in polymer foam processing systems

ABSTRACT

Methods and systems that include introducing blowing agent into a hopper of a polymeric foam processing system.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/926,882, filed Mar. 20, 2018, and is a continuation-in-partof U.S. patent application Ser. No. 15/909,873, filed Mar. 1, 2018, bothof which are incorporated herein by reference in their entireties forall purposes.

TECHNICAL FIELD

The present application relates generally to polymer foam processingand, more particularly, to methods and systems that include introducingblowing agent into a hopper of a polymeric foam processing system.

BACKGROUND

Polymeric foams include a plurality of voids, also called cells, in apolymer matrix. Polymeric foams are processed using a variety oftechniques. For example, polymeric foams can be processed by injecting aphysical blowing agent into the polymeric material within an extruder.For instance, many conventional systems inject blowing agent through ablowing agent port in the barrel of the extruder into a fluid stream ofpolymeric material within the extruder. The blowing agent may be mixedwith the polymeric material to form a solution within the extruder. Thesolution may be, for example, injected into a mold to form an injectionmolded polymeric foam article. Such conventional systems may requiremodifications to standard extruder equipment (e.g., to extend length ofthe barrel to ensure sufficient mixing, to form a blowing agent port,etc.) and/or utilize relatively expensive equipment (e.g., blowing agentmass flow meter) to control the flow and introduction of blowing agentinto the extruder.

Other prior art systems have attempted to simplify the design of polymerfoam processing systems and reduce their costs. For example, certainsystems have introduced physical blowing agent into a hopper of theextruder. Such systems generally have not controlled the amount ofblowing agent introduced into the polymeric material. For certain foamprocesses, such an approach to blowing agent delivery may be adequate.However, in other processes that require relatively precise control overblowing agent delivery, such an approach may not be adequate.

Accordingly, there is a need for new blowing agent introductiontechniques that may be used with polymer foam systems and methods.

SUMMARY

Methods and systems including introducing blowing agents into a hopperof a polymeric foam processing system are described.

In one aspect, a method is provided. The method comprises providing ahopper of a polymeric foam processing system. The method furthercomprises supplying polymeric material to the hopper, supplying chemicalblowing agent to the hopper and supplying physical blowing agent to thehopper. The method further comprises supplying polymeric material,chemical blowing agent and physical blowing agent to an inlet of anextruder including a screw configured to rotate in a barrel. The methodfurther comprises conveying a mixture of polymeric material, chemicalblowing agent and physical blowing agent in a downstream direction inthe extruder. The method further comprises accumulating a shot of themixture of polymeric material and blowing agent and injecting the shotinto a mold to form a molded polymeric foam article.

In one aspect, a system is provided. The system comprises an extruderincluding a screw configured to rotate in a barrel to convey a mixtureof polymeric material and blowing agent in a downstream direction in apolymer processing space defined between the screw and the barrel. Thesystem further comprises a mold connected to an outlet of the extruder.The screw is configured to periodically move in a downstream directionin the barrel to inject a shot of the mixture of polymeric material andblowing agent into the mold. The system further comprises a hopperconfigured to hold polymeric material pellets and blowing agent in achamber volume. The hopper includes at least one inlet connectable to asource of the blowing agent. The hopper includes an outlet connectableto the polymer processing space in the extruder. The system furthercomprises a pressure regulator constructed and arranged to control thepressure of blowing agent supplied to the hopper. The system furthercomprises at least one processor and at least one storage medium havingencoded thereon executable instructions that, when executed by the atleast one processor, cause the at least one processor to carry out amethod which comprises controlling a pressure of the blowing agentsupplied to the hopper to a desired pressure using the pressureregulator based, at least in part, on the desired weight percentage ofblowing agent in the shot of the mixture of polymeric material andblowing agent.

In one aspect, a method is provided. The method comprises providing ahopper configured to hold polymeric material pellets and supplyingblowing agent to the hopper at a desired blowing agent pressure based,at least in part, on a desired weight percentage of blowing agent in theshot. The method further comprises supplying blowing agent and thepolymeric material pellets to an inlet of an extruder including a screwconfigured to rotate in a barrel. The method further comprises conveyinga mixture of polymeric material and the blowing agent in a downstreamdirection in the extruder and accumulating a shot of the mixture ofpolymeric material and blowing agent. The method further comprisesinjecting the shot into a mold to form a molded polymeric foam article.

In one aspect, a system is provided. The system includes an extruderincluding a screw configured to rotate in a barrel to convey a mixtureof polymeric material and blowing agent in a downstream direction in apolymer processing space defined between the screw and the barrel. Thesystem further includes a mold connected to an outlet of the extruder.The screw is configured to periodically move in a downstream directionin the barrel to inject a shot of the mixture of polymeric material andblowing agent into the mold. The system further comprises a blowingagent introduction system including a source of blowing agent and apressure regulator. The system further comprises a hopper including achamber volume having a port fluidly connected to the source of blowingagent. The hopper is configured to hold polymeric material pellets andblowing agent in a chamber volume. The hopper includes a first outletconfigured to supply polymeric material pellets and blowing agent to thepolymer processing space in the extruder. The system is configured torecycle blowing agent in the chamber volume to a location in the blowingagent introduction system upstream of the pressure regulator.

In one aspect, a system is provided. The system includes an extruderincluding a screw configured to rotate in a barrel to convey a mixtureof polymeric material and blowing agent in a downstream direction in apolymer processing space defined between the screw and the barrel. Thesystem further includes a mold connected to an outlet of the extruder.The screw is configured to periodically move in a downstream directionin the barrel to inject a shot of the mixture of polymeric material andblowing agent into the mold. The system further includes a blowing agentintroduction system including a source of blowing agent and a hopperincluding at least a first chamber volume and a second chamber volume.At least one of the first or the second chamber volumes are configuredto connect to the source of blowing agent and to hold polymeric materialpellets and blowing agent.

Other aspects and features will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a polymer foam processing systemaccording to an embodiment.

FIG. 2 schematically illustrates a multi-chamber hopper assemblyaccording to an embodiment.

FIG. 3 schematically illustrates a computing device suitable for use inconnection with a polymer foam processing system according to anembodiment.

DETAILED DESCRIPTION

Methods and systems that include introducing blowing agent into a hopperof a polymeric foam system are described. The methods and systems mayinclude introducing chemical blowing agent, as well as physical blowingagent, into the hopper. It has been observed that introducing bothchemical and physical blowing agents into the hopper may be particularlyadvantageous in some cases. For example, using physical blowing agentmay reduce the amount of chemical blowing agent that otherwise would beused to achieve a certain density reduction in the resulting foamedarticle which can lead to cost savings. Also, using chemical blowingagent may reduce the pressure and/or amount of physical blowing agentrequired to achieve a certain density reduction and/or article quality(e.g., lack of warp). Such reduction in pressure and/or amount ofphysical blowing agent can lead to blowing agent cost savings and/or theability to use less complicated and expensive equipment (e.g., gasseals). The methods and systems are particularly well suited forprocesses that produce injection molded polymeric foam articles.

In some embodiments, the methods may utilize a control system thatenhances control over the amount of physical blowing agent (e.g.,nitrogen, carbon dioxide) introduced into the polymeric material beingprocessed by the system. As described further below, the system maycontrol the amount of physical blowing agent introduced, in part, bycontrolling the pressure of blowing agent supplied to the hopper to adesired amount. The desired pressure may be based, at least in part, onthe desired weight percentage of physical blowing agent in the polymericmaterial being processed. As described further below, the methods maydetermine the desired blowing agent pressure from a variety ofadditional inputs which may relate to the blowing agent (e.g., blowingagent type), desired article characteristics (e.g., article weight),polymer characteristics (e.g., polymer type, polymer pellet bulkdensity) and equipment design (e.g., hopper chamber volume). In someembodiments, the methods and systems are designed to recycle blowingagent to reduce the amount of unused blowing agent. The methods andsystems may also include a multi-chamber hopper design that facilitatesre-filling the chamber(s) with polymeric material pellets, for example,when a chamber is empty.

Referring to FIG. 1, a blowing agent introduction system 10 is used todeliver physical blowing agent to a polymer processing system 12. Inthis embodiment, system 12 is an injection molding system that includesan extruder 14 and a mold 16. Polymeric material (e.g., in the form ofpellets) is provided to a hopper 18. As described further below,chemical blowing agent is also provided to the hopper. The hoppersupplies the chemical blowing agent, physical blowing agent andpolymeric material to the extruder.

The extruder includes a screw 20 designed to rotate within a barrel 22to process the polymeric material. Heat (e.g., provided by heaters onthe extruder barrel) and shear forces (e.g., provided by the rotatingscrew) act to melt the polymeric material to form a fluid polymericstream which is conveyed in a downstream direction in the extruder byrotation of the screw. Such heat and shear forces also cause thechemical blowing agent to react (e.g., by decomposing) to form carbondioxide which may be present in the fluid stream in the supercriticalstate within the extruder. The physical blowing agent (e.g., nitrogen)may also be present in the fluid stream in the supercritical statewithin the extruder.

In some embodiments, the mixture is a single-phase solution with thephysical blowing agent being dissolved in the polymeric material priorto injection into the mold. In the illustrated embodiment, a valve 29 isarranged between the outlet of the extruder and the inlet of the mold. Ashot of the mixture (e.g., single-phase solution) may be accumulateddownstream of the screw within the extruder causing the screw to retractin an upstream direction within the barrel. When suitable conditionshave been reached (e.g., after a predetermined time period, at apredetermined screw position, etc.), the screw stops retracting androtating to end the plastication period of the molding cycle. During theinjection period of the molding cycle, the screw may be forceddownstream within the barrel to inject the mixture into a cavity of themold when valve 29 opens. The mixture is subjected to a pressure dropduring injection which nucleates a large number of cells and a polymerfoam article is formed in the mold. The screw may begin to rotate onceagain to begin another molding cycle. The method is typically repeatedto produce multiple polymeric foam articles.

It should also be understood that not all methods described hereininvolve formation of a single-phase solution and that certain methodsmay involve injection of a two-phase mixture (e.g., polymeric materialand blowing agent) into the mold. It may be preferred in certainembodiments that produce microcellular foam articles, as describedfurther below, to form a single-phase solution which is nucleated uponinjection into the mold. Suitable processes for forming single-phasesolutions and nucleating upon injection into the mold have beendescribed in commonly-owned U.S. Pat. No. 6,884,823 which isincorporated herein by reference above in its entirety.

It should be understood that the polymer foam processing system mayinclude a number of conventional components not illustrated in thefigure. Though the physical blowing agent introduction system isillustrated as being used in conjunction with an injection moldingsystem, it should be understood that the blowing agent introductionsystem may be used in conjunction with any other polymer processingsystem into which blowing agent is introduced including blow moldingsystems.

In general, methods described herein may utilize any suitable chemicalblowing agent. For example, suitable chemical blowing agent may becapable of producing carbon dioxide under conditions in the extruder.The chemical blowing agent may undergo a reaction (e.g., a decompositionreaction) to form carbon dioxide upon being heated in the extruder.Suitable chemical blowing agents may include acids and/or alkalis. Insome embodiments, suitable chemical blowing agent may comprise citricacid, sodium bicarbonate, monosodium citrate, dinitrosopentamethylenetetramine (DPT), oxybis (benzenesulfonyl hydrazide)(OBSH), p-toluenesulfonyl hydrazide (TSH), p-toluenesulfonylsemicarbazide (TSS) and calcium carbonate. It should be understood thatthe reactions that produce carbon dioxide may also produce otherby-products which may be detectable in the final molded article.

As described herein, the inventors have appreciated that using certainamounts of chemical blowing agent (e.g., in combination with certainamounts of nitrogen physical blowing agent) may be preferred to forminjection molding articles having desirable characteristics. Forexample, it may be preferred for the weight percentage of chemicalblowing agent to be between about 0.10 and 2.0 weight percent based onthe total weight of the polymeric material. In some of theseembodiments, the weight percentage of the chemical blowing agent may begreater than or equal to 0.3 weight percent or greater than or equal0.50 weight percent based on the total weight of the polymeric material;and, in some embodiments, the weight percentage may be less than orequal to 2.0 weight percent and/or less than or equal to 1.0 and/or lessthan or equal to 0.5 weight percent based on the total weight ofpolymeric material. It should be understood that any suitable rangesdefined by the above-noted minimum and maximum values may be used (e.g.,between 0.30 weight percent and 2.0 weight percent).

The chemical blowing agents used in the methods described herein mayhave any suitable form. In some cases, the chemical blowing agents maybe in the form of pellets. In some cases, the chemical blowing agentsmay be in the form of particles. Other forms may also be also suitablesuch as flakes, powder or liquid. It should also be understood that thepellets and/or particles (or other forms) may include other components(e.g., non-reactive components) in addition to the chemical blowingagent. In some cases, the particles may have small particle sizes suchas less than 10 micron and/or less than 1 micron. For example, some suchchemical blowing agent particles have been described in U.S. Pat. No.8,563,621 which is incorporated herein by reference in its entirety.

The physical blowing agent introduction system includes a physicalblowing agent source 26 connectable to one or more port(s) 28 that areconnectable to a chamber volume in the hopper. Conduit 36 is used toconnect various components of the introduction system and to provide apathway from the source to the blowing agent port(s). In theillustrative embodiment, upstream of the hopper, the blowing agentintroduction system includes a pressure regulator 38 which, as describedfurther herein, may be used to set the pressure of blowing agentsupplied to the hopper at a desired level. In some embodiments, theblowing agent introduction system may include an accumulator 47connected to an interchangeable bottle of blowing agent. In someembodiments, such as when a bottle does not supply blowing agent at asufficiently high pressure, a pump may be connected to increase and/ormaintain pressure of blowing agent in the introduction system. A controlsystem 44 of the physical blowing agent introduction system may receiveone or more inputs (e.g., relating to the desired amount of physicalblowing agent introduced into the polymeric material which may beselected by an operator) and can provide output(s) to control thepressure regulator to supply a desired physical blowing agent pressureto the hopper. It should be understood that the blowing agentintroduction system may include other standard components such as valveswhich may be used to selectively control blowing agent flow therepast.As described further below, the physical blowing agent introductionsystem may be configured to recycle residual blowing agent remaining inthe hopper. It should also be understood that the physical blowing agentintroduction system may have other designs and may not include all ofthe components (e.g., a control system) as described herein in allembodiments.

The control system may be any of the type known in the art such as acomputing device, as described further below. As described above, thecontrol system is capable of receiving input signals (e.g., from a user,from other components of the polymer processing system) and sendingappropriate output signals (e.g., to components of the blowing agentintroduction system such as the pressure regulator and/or the polymerprocessing system).

As noted above, techniques described herein may involve supplyingphysical blowing agent to the hopper at a desired pressure. Such anapproach may be used to supply a desired amount of physical blowingagent into the polymeric material (e.g., desired weight percentage ofphysical blowing agent in the shot of polymeric material injected intothe mold) which, for example, may be selected (e.g., as a value that isinputted to the system) by a user. As described further below, thedesired pressure may be determined from a number of parameters inaddition to the desired weight percentage of blowing agent in thepolymeric material.

In some embodiments, the parameters may include characteristics relatingto the equipment design. For example, the hopper chamber volume may beused as a parameter.

In some embodiments, the parameters may include characteristics relatingto the polymeric material. For example, the type of polymer (e.g., resintype such as polypropylene, polyethylene, etc.), weight of polymericmaterial and/or polymeric material density may be used as parameter(s).

In some embodiments, the parameters may include characteristics relatingto the injected molded article. For example, the weight (e.g., mass ofpolymeric material) of the injection molded article may be used.

In some embodiments, the parameters may include characteristics relatingto the physical blowing agent. For example, the type of physical blowingagent (e.g., nitrogen, carbon dioxide) may be a parameter that is usedin addition to the desired weight percentage of physical blowing agentin the polymeric material noted above.

In some embodiments, one aspect of determining the desired physicalblowing agent pressure supplied to the hopper involves a step ofdetermining the volume of physical blowing agent in the chamber in thehopper.

In some embodiments, one aspect of determining the desired physicalblowing agent pressure supplied to the hopper involves a step ofdetermining the amount of physical blowing agent that leaks out of thechamber volume of the hopper.

In some embodiments, one aspect of determining the desired physicalblowing agent pressure supplied to the hopper involves a step ofdetermining the maximum number of shots that may be achieved when usinga hopper having a certain chamber volume.

The systems and methods described herein system may be used to introducephysical blowing agent into polymeric material within the extruder overa wide range of desired amounts. The desired physical blowing agentamount depends upon the particular process and is generally less thanabout 10% by weight of polymeric material and physical blowing agent. Inmany embodiments, the physical blowing agent level is less than about5%, in others, less than about 3%, in others less than about 1%, inothers less than about 0.5%, and still others less than about 0.1%, oreven lower by weight of polymeric material and blowing agent mixture. Asnoted above, in some embodiments, it is possible to use relatively lowamounts of physical blowing agent when chemical blowing agents are alsoused to achieve results that otherwise would require higher amounts ofphysical blowing agent. In some such embodiments, using low amounts ofphysical blowing agents has advantages such as cost savings.

During an illustrative process, the source provides physical blowingagent to the introduction system. The source may supply any type ofphysical blowing agent known to those of ordinary skill in the artincluding nitrogen, carbon dioxide, hydrocarbons, chlorofluorocarbons,noble gases and the like or mixtures thereof. The blowing agent may besupplied in any flowable physical state such as a gas, a liquid, or asupercritical fluid. According to one preferred embodiment, the sourceprovides nitrogen as a blowing agent. In another preferred embodiment,the source provides carbon dioxide as a blowing agent. In certainembodiments, solely carbon dioxide or nitrogen is used. Blowing agentsthat are in the supercritical fluid state after injection into theextruder, (optionally, before injection as well) and in particularsupercritical carbon dioxide and supercritical nitrogen, are preferredin certain embodiments.

In some embodiments and as illustrated, the system is designed torecycle unused blowing agent. For example, the system may be configuredto recycle residual physical blowing agent remaining in the chambervolume in the hopper after the polymeric material in the hopper havebeen supplied to the extruder. In some cases, the residual blowing agentis removed from the hopper (e.g., via a port in the chamber volume) andre-circulated back into the blowing agent introduction system so that itmay be used again. As shown in FIG. 1, the physical blowing agent may bere-circulated via conduit 46. Conduit 46, for example, re-introduces thephysical blowing agent into the physical blowing agent introductionsystem at a position upstream of the pressure regulator. In someembodiments, the physical blowing agent is re-introduced into anaccumulator of the physical blowing agent introduction system. In someembodiments, re-circulated physical blowing agent may be re-introducedinto the chamber volume of the hopper that contains unused polymericmaterial (e.g., pellets).

In some embodiments, the polymer foam processing system includes ahopper having multiple chambers. For example, FIG. 2 schematicallyillustrates a multi-chamber hopper assembly 100 according to anembodiment. The multi-chamber hopper assembly, as shown, includes afirst chamber 102 and a second chamber 104. The first and secondchambers are connected to a source of polymeric material (e.g., pellets)and/or a source of chemical blowing agent. In some cases, and as shown,the hopper assembly includes a loader 106 which is configured to containpolymeric material and chemical blowing agent upstream of the hopperchambers. The assembly may include respective shut-off valves 108arranged between the loader and inlets to the chambers which may becontrolled to permit or prevent polymeric material and chemical blowingagent from entering the chambers. The assembly may also include physicalblowing agent inlets 112 which are fluidly connected to the blowingagent source. Shut-off valves may be associated with inlets 112 topermit or prevent physical blowing agent from flowing into the chambers.Shut-off valves 114 may also be positioned at respective outlets 115,117 of the chambers. In the illustrative embodiment, the outlets areconnected to a third chamber 116. During use, one of outlet shut-offvalves is open to permit supply of polymeric material (and blowingagents) to the third chamber, while the other of the outlet shut-offvalves is closed to prevent supply of polymeric material and blowingagents to the third chamber. When all of the polymeric material is usedfrom one of the chambers the appropriate outlet valve is closed and theother outlet valve is opened to enable the other chamber to supplypolymeric material and chemical blowing agent to the third chamber. Thethird chamber includes an outlet 118 that is connected to the polymerprocessing space so that polymeric material pellets and blowing agentmay be supplied to the extruder. As illustrated, the third chamber alsoincludes a physical blowing agent inlet that is fluidly connected to theblowing agent source.

Pressure may be maintained within the chambers that are supplying thepolymeric material and blowing agent to the extruder and reduced in theother chamber. That is, when the outlet of the first chamber is open andthe outlet of the second chamber is closed, pressure may be maintainedin the first chamber and the third chamber and may be reduced in thesecond chamber (e.g., to atmosphere, for example, to enable polymericmaterial to be added to the second chamber). Similarly, when the outletof the second chamber is open and the outlet of the first chamber isclosed, pressure may be maintained in the second chamber and the thirdchamber and may be reduced in the first chamber (e.g., to atmosphere,for example, to enable polymeric material pellets to be added to thesecond chamber). When pressure is reduced in one or more chambers, itmay be accomplished by releasing the physical blowing agent from thechamber. In some cases, the released physical blowing agent may berecycled as described above.

It should be understood that the multi-chamber hopper assembly mayinclude additional components that are not illustrated. In someembodiments, blowing agent is not supplied to first chamber 102 orsecond chamber 104 and is only supplied to third chamber. In suchembodiments, the first chamber and second chamber may not includeblowing agent ports, while the third chamber may include a physicalblowing agent port. It also should be understood that not allembodiments utilize a multi-chamber hopper assembly and that a moreconventional (e.g., single chamber) hopper assembly may be used in somecases.

Any polymeric material suitable for forming polymeric foams may be usedwith the methods described herein. Such polymeric materials, in somecases, are thermoplastics which may be amorphous, semicrystalline, orcrystalline materials. In some embodiments, semicrystalline orcrystalline materials are preferred. Typical examples of polymericmaterials used include polyolefins (e.g., polyethylene andpolypropylene), styrenic polymers (e.g., polystyrene, ABS),fluoropolymers, polyamides, polyimides, polyesters, and/or mixtures ofsuch polymeric materials. In some embodiments, polyolefin materials maybe used. In some such embodiments, the polyolefin material may be amixture of more than one type of olefin, or a mixture of one or moretypes of polyolefin and one or more types of non-polyolefin polymericmaterials. The polymeric material used may depend upon the applicationin which the article is ultimately utilized.

In general, the polymeric foam articles have a certain cell size. Insome embodiments, the methods described herein may be used to producefoam articles having a small cell size. For example, in some cases, themethods involve production of microcellular foam articles. Themicrocellular foam article may have an average cell size of less than100 microns. In some cases, the microcellular foam articles have anaverage cell size of less than 75 microns. Average cell size may bedetermined by measuring a representative number of cells usingmicroscopy (e.g., SEM) techniques. In some embodiments (includingembodiments involving production of microcellular foam material), thecell size may vary across the thickness of the injection molded article.For example, the cell size at or near the center of the article may belarger than the cell size approaching edges of the article and/or edgesof the foamed region of the article.

It should be understood that not all methods described herein involveproducing microcellular foam and that, in some embodiments, articleshaving an average cell size of greater than 100 microns.

The injection molded polymeric foam articles may have a range of voidvolume percentages. As used herein, the void volume percentage is thepercentage of the volume of an article occupied by voids. It can bemeasured by the following equation:Void volume %=100×[1−(density of the polymer foam article/density ofsolid polymer)]

For example, if the foam article has a density of 0.85 g/cm³ and thesolid polymer has a density of 1.0 g/cm³, then the percentage voidvolume is 15%. The particular void volume may depend upon theapplication. In some embodiments, the void volume percentage isrelatively low. For example, the void volume percentage may be less than20%, less than 15%, less than 12%, less than 10% or less than 5%. Insome embodiments, the void volume may be greater than 2%; greater than5%, greater than 8%, greater than 10% or greater than 15%. It should beunderstood that any suitable ranges defined by the above-noted minimumand maximum values may be used (e.g., between 2% and 15%, between 5% and15%, between 8% and 12%, etc.).

In general, the injection molded polymeric foam articles may have anysuitable wall thickness. As used herein, wall thickness refers to thepredominant cross-sectional dimension across the thickness of thearticle. For example, the article thickness may be less than 5.0 mm,less than 3.0 mm, less than 2.5 mm, less than 2.0 mm or less than 1.0mm. In some embodiments, the article thickness may be greater than 0.5mm, greater than 1.0 mm or greater than 1.5 mm. It should be understoodthat any suitable ranges defined by the above-noted minimum and maximumvalues may be used (e.g., between 0.5 mm and 5 mm, between 0.5 mm and3.0 mm, between 1.0 mm and 3.0 mm, etc.).

As described above, in some embodiments, the injection molded polymericfoam articles may have unfoamed skin region(s) extending from theexterior surfaces of the article (e.g., article surfaces that are incontact with the injection mold). The skin regions may surround (atleast in part) a foamed interior region. The total skin thickness and/orpercentage of total skin thickness compared to total wall thickness maybe characterized using visual techniques (e.g., by eye and/ormicroscopy). The total skin thickness is the sum of the skin thicknessesacross the cross-sectional thickness of the article.

In some embodiments, the total skin thickness may be greater than 100microns, greater than 200 microns, greater than 250 microns, greaterthan 300 microns, greater than 400 microns or greater than 500 microns.In some embodiments, the total skin thickness may be less than 700microns, less than 600 microns, less than 500 microns or less than 300microns. It should be understood that any suitable ranges defined by theabove-noted minimum and maximum values may be used (e.g., between 100microns and 500 microns, between 250 microns and 700 microns, etc.).

In some embodiments, the percentage of total skin thickness compared tototal wall thickness may be greater than 15%, greater than 25%, greaterthan 40%, greater than 50% or greater than 60%. In some embodiments, thepercentage of total skin thickness compared to total wall thickness maybe less than 70%, less than 50%, less than 40% or less than 25%. Itshould be understood that any suitable ranges defined by the above-notedminimum and maximum values may be used (e.g., between 25% and 70%,between 15% and 50%, etc.).

It should be understood that not all injection mold articles describedherein have an identifiable skin. That is, such articles may comprisesubstantially entirely of a foamed structure.

The injection molded articles described herein can exhibit excellentproperties including excellent mechanical properties such as highelongations. For example, the percent elongation at break (as measuredby ASTM D638) may be greater than 5%, greater than 25%, greater than50%, greater than 100%, or greater than 150%. In some embodiments, thepercent elongation at break (as measured by ASTM D638) may be less than200%, less than 150%, less than 100% or less than 50%. It should beunderstood that any suitable ranges defined by the above-noted minimumand maximum values may be used (e.g., between 5% and 200%, between 25%and 150%, etc.).

The desirable properties and characteristics enable the injection moldedfoam articles described herein to be used in a variety of applications.In particular, the articles may be used in a variety of consumer andindustrial goods including automotive components and packaging.

In some embodiments, the techniques described herein may be embodied incomputer-executable instructions implemented as software, including asapplication software, system software, firmware, middleware, embeddedcode, or any other suitable type of computer code. Suchcomputer-executable instructions may be written using any of a number ofsuitable programming languages and/or programming or scripting tools,and also may be compiled as executable machine language code orintermediate code that is executed on a framework or virtual machine.

When techniques described herein are embodied as computer-executableinstructions, these computer-executable instructions may be implementedin any suitable manner, including as a number of functional facilities,each providing one or more operations to complete execution ofalgorithms operating according to these techniques. A “functionalfacility,” however instantiated, is a structural component of a computersystem that, when integrated with and executed by one or more computers,causes the one or more computers to perform a specific operational role.A functional facility may be a portion of or an entire software element.For example, a functional facility may be implemented as a function of aprocess, or as a discrete process, or as any other suitable unit ofprocessing. If techniques described herein are implemented as multiplefunctional facilities, each functional facility may be implemented inits own way; all need not be implemented the same way. Additionally,these functional facilities may be executed in parallel and/or serially,as appropriate, and may pass information between one another using ashared memory on the computer(s) on which they are executing, using amessage passing protocol, or in any other suitable way.

Generally, functional facilities include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Typically, the functionalityof the functional facilities may be combined or distributed as desiredin the systems in which they operate. In some implementations, one ormore functional facilities carrying out techniques herein may togetherform a complete software package. These functional facilities may, inalternative embodiments, be adapted to interact with other, unrelatedfunctional facilities and/or processes, to implement a software programapplication. In other implementations, the functional facilities may beadapted to interact with other functional facilities in such a way asform an operating system. In other words, in some implementations, thefunctional facilities may be implemented alternatively as a portion ofor outside of an operating system.

Some exemplary functional facilities have been described herein forcarrying out one or more tasks. It should be appreciated, though, thatthe functional facilities and division of tasks described is merelyillustrative of the type of functional facilities that may implement theexemplary techniques described herein, and that embodiments are notlimited to being implemented in any specific number, division, or typeof functional facilities. In some implementations, all functionality maybe implemented in a single functional facility. It should also beappreciated that, in some implementations, some of the functionalfacilities described herein may be implemented together with orseparately from others (i.e., as a single unit or separate units), orsome of these functional facilities may not be implemented.

Computer-executable instructions implementing the techniques describedherein (when implemented as one or more functional facilities or in anyother manner) may, in some embodiments, be encoded on one or morecomputer-readable media to provide functionality to the media.Computer-readable media include magnetic media such as a hard diskdrive, optical media such as a Compact Disk (CD) or a Digital VersatileDisk (DVD), a persistent or non-persistent solid-state memory (e.g.,Flash memory, Magnetic RAM, etc.), or any other suitable storage media.Such a computer-readable medium may be implemented in any suitablemanner, including as computer-readable storage media 806 of FIG. 3described below (i.e., as a portion of a computing device 800) or as astand-alone, separate storage medium. As used herein, “computer-readablemedia” (also called “computer-readable storage media”) refers totangible storage media. Tangible storage media are non-transitory andhave at least one physical, structural component. In a“computer-readable medium,” as used herein, at least one physical,structural component has at least one physical property that may bealtered in some way during a process of creating the medium withembedded information, a process of recording information thereon, or anyother process of encoding the medium with information. For example, amagnetization state of a portion of a physical structure of acomputer-readable medium may be altered during a recording process.

In some, but not all, implementations in which the techniques may beembodied as computer-executable instructions, these instructions may beexecuted on one or more suitable computing device(s) operating in anysuitable computer system, including the exemplary computer system ofFIG. 3, or one or more computing devices (or one or more processors ofone or more computing devices) may be programmed to execute thecomputer-executable instructions. A computing device or processor may beprogrammed to execute instructions when the instructions are stored in amanner accessible to the computing device or processor, such as in adata store (e.g., an on-chip cache or instruction register, acomputer-readable storage medium accessible via a bus, acomputer-readable storage medium accessible via one or more networks andaccessible by the device/processor, etc.). Functional facilitiescomprising these computer-executable instructions may be integrated withand direct the operation of a single multi-purpose programmable digitalcomputing device, a coordinated system of two or more multi-purposecomputing device sharing processing power and jointly carrying out thetechniques described herein, a single computing device or coordinatedsystem of computing devices (co-located or geographically distributed)dedicated to executing the techniques described herein, one or moreField-Programmable Gate Arrays (FPGAs) for carrying out the techniquesdescribed herein, or any other suitable system.

FIG. 3 illustrates one exemplary implementation of a computing device inthe form of a computing device 800 that may be used in a systemimplementing techniques described herein, although others are possible.It should be appreciated that FIG. 3 is intended neither to be adepiction of necessary components for a computing device to operate inaccordance with the principles described herein, nor a comprehensivedepiction.

Computing device 800 may comprise at least one processor 802, a networkadapter 804, and computer-readable storage media 806. Computing device800 may be, for example, a desktop or laptop personal computer, apersonal digital assistant (PDA), a smart mobile phone, a server, awireless access point or other networking element, or any other suitablecomputing device. Network adapter 804 may be any suitable hardwareand/or software to enable the computing device 800 to communicate wiredand/or wirelessly with any other suitable computing device over anysuitable computing network. The computing network may include wirelessaccess points, switches, routers, gateways, and/or other networkingequipment as well as any suitable wired and/or wireless communicationmedium or media for exchanging data between two or more computers,including the Internet. Computer-readable media 806 may be adapted tostore data to be processed and/or instructions to be executed byprocessor 802. Processor 802 enables processing of data and execution ofinstructions. The data and instructions may be stored on thecomputer-readable storage media 806.

The data and instructions stored on computer-readable storage media 806may comprise computer-executable instructions implementing techniqueswhich operate according to the principles described herein. In theexample of FIG. 3, computer-readable storage media 806 storescomputer-executable instructions implementing various facilities andstoring various information as described above. Computer-readablestorage media 806 may store the various processes/facilities discussedabove.

While not illustrated in FIG. 3, a computing device may additionallyhave one or more components and peripherals, including input and outputdevices. These devices can be used, among other things, to present auser interface. Examples of output devices that can be used to provide auser interface include printers or display screens for visualpresentation of output and speakers or other sound generating devicesfor audible presentation of output. Examples of input devices that canbe used for a user interface include keyboards, and pointing devices,such as mice, touch pads, and digitizing tablets. As another example, acomputing device may receive input information through speechrecognition or in other audible format.

Embodiments have been described where the techniques are implemented incircuitry and/or computer-executable instructions. It should beappreciated that some embodiments may be in the form of a method, ofwhich at least one example has been provided. The acts performed as partof the method may be ordered in any suitable way. Accordingly,embodiments may be constructed in which acts are performed in an orderdifferent than illustrated, which may include performing some actssimultaneously, even though shown as sequential acts in illustrativeembodiments.

The function and advantage of these and other embodiments of the presentinvention will be more fully understood from the examples below. Thefollowing example is intended to illustrate the benefits of the presentinvention, but does not exemplify the full scope of the invention andshould not be considered limiting in this regard.

Various aspects of the embodiments described above may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Having thus described several aspects of at least one embodiment, it isto be appreciated that various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe principles described herein. Accordingly, the foregoing descriptionand drawings are by way of example only.

What is claimed:
 1. A method comprising: providing a hopper of a polymerfoam processing system; supplying polymeric material to the hopper;supplying chemical blowing agent to the hopper; supplying physicalblowing agent to the hopper, wherein the physical blowing agent issupplied to the hopper at a pressure of less than 40 bar; supplying thepolymeric material, chemical blowing agent and physical blowing agent toan inlet of an extruder including a screw configured to rotate in abarrel; conveying a mixture of polymeric material, chemical blowingagent and physical blowing agent in a downstream direction in theextruder; accumulating a shot of the mixture of polymeric material andblowing agent; and injecting the shot into a mold to form a moldedpolymeric foam article.
 2. The method of claim 1, wherein the weightpercentage of the chemical blowing agent in the mixture is less than orequal to 1.0 weight percent of the polymeric material in the mixture. 3.The method of claim 1, wherein the physical blowing agent comprisesnitrogen.
 4. The method of claim 1, wherein the weight percentage of thephysical blowing agent in the mixture is less than or equal to 1.0percent of the weight of the polymeric material in the mixture.
 5. Themethod of claim 1, wherein the physical blowing agent is supplied to thehopper at a desired physical blowing agent pressure based, at least inpart, on a desired weight percentage of blowing agent in the shot. 6.The method of claim 1, further comprising determining the desiredphysical blowing agent pressure, in part, from the volume of physicalblowing agent in the hopper.
 7. The method of claim 1, furthercomprising moving the screw in a downstream direction in the barrel toinject the shot into the mold.
 8. The method of claim 1, wherein thearticle has a void volume of at least 10%.
 9. The method of claim 1,wherein the hopper includes multiple chambers.
 10. The method of claim1, wherein the chemical blowing agent reacts to form carbon dioxidewhile conveying the mixture.
 11. The method of claim 1, wherein thepolymeric material is supplied to the hopper in the form of pellets. 12.The method of claim 1, wherein the chemical blowing agent is supplied tothe hopper in the form of pellets and/or particles.